I've ridden MX Style up to -20 with -40 windchill in minnesota. As long as you get your skin covered up you are fine. Frostbite is the real risk...not warmth. Your head generates plenty of heat to keep you warm in any helmet. if it is under 30, I wear a no-fog, which protects below the eyes. if it gets under 10 or 0 F, I will put a piece of race tape (colored duct tape, across my forehead over my balaclava(very thin version).
Just gotta have the right gear.... no-fog, thin bala, and a roll of duct tape of course!!
it is way better than the other helmets...once you get used to it, it is impossible to go back.
kj